Phase sensitive alternating current track circuit



April 28, 1959 c. E. STAPLES PHASE SENSITIVE ALTERNATING CURRENT TRACKCIRCUIT Filed Sept. 21. 1956 5 Sheets-Sheet 1 INVENTOR.

Crawford E. Staples. M k .W

H15 AWFORMEX April 28, 1959 C. E. STAPLES Filed Sept. 21. 1956 5Sheets-Sheet 2 Qmdmuz I. -Qaad an 25 Maglzeiomol lje Force.

Z4 Z5 Winding b. 52 9 51 2 Abnmal fi'ck'Q0 Kesultazz M new 15 (WE)mozzue lbr'ae. lZeue se PL'CK U U Track 26 I Voltage.

I I I9 35 Qaaa'l'an E. Qaadlan 1F Resalm Magneomozk/e Force.

Maglzeomoa've Force.

Wlbdrlyb Z5 51 27 -----/V01 12r2wzl Peck U11 Trudi Vbliage. 2 "gel/easeFad 17))- Wmdny a.

Quad cm INVENTOR. Lmwfiord E Saples.

HIS ATTORNEY April 28, 1959 c. E. STAPLES PHASE SENSITIVE ALTERNATINGCURRENT TRACK CIRCUIT Filed Sept. 21. 1956 5 Sheets-Sheet 3 8' .o "J g 5K) 5 5, id

INVENTOR.

Crazy/bra E 52290605. BY LM April 28, 1959 Filed Sept. 21. 1956 c. E.STAPLES 2,884,516

PHASE SENSITIVE ALTERNATING CURRENT TRACK CIRCUIT 5 Sheets-Sheet 4INVENTOR. CPtlLl/[bld E Sgoles BY MAW lemadzg au mzz Source HIS 41mm YApril 28, 195 c. E. STAPLES 2,884,516

PHASE SENSITIVE ALTERNATING CURRENT TRACK CIRCUIT Filed Sept. 21. 1956 5Sheets-Sheet 5 m" r 9 a a g g N o w. a "U Q *1 5 5 5 0 INVENTOR.

CzvauQ/Zwd l. Sryaks. M k m,

115 gmmozzwr S tes. Pat

PHASE SENSITIVE ALTERWATIN G CURRENT TRACK CIRCUIT 1 ApplicationSeptember 21, 1956, Serial No. 611,330

' 5 Claims. c1. 246-34 My invention relates to a phase sensitivealternating current track circuit for use in connection with railwaySignaling systems. More particularly, my invention relates to animprovement 'upon the track circuit shown and described in LettersPatent of the United States No. 2,585,505, issued February 12, 1952, toD. G. Shipp.

I One of the problems encountered in the use of alternating currenttrack circuits in connection with railway signaling systems is that ofpreventing improper operation of the track signals associated with thesignaling system, due to currents feeding across detective insulatedrail joints. The failure of such insulated rail joints is particularlydangerous in signaling systems in which the track sections are separatedby insulated joints in one rail only or in systems in which the sectionsare sepa' rated by insulated joints in both rails and with adjoiningtrack sections connected with impedance bonds, the impedance bondsproviding a return path for traction current in electrified railwayterritory. In either case, the failure of asingle insulated rail jointmight permit thedull-tracl; voltage of an adjoining track section tofeed across a defective insulated joint and the impedance bond to causeimproper operation of the track signals.

Previously, protection against such effects has been providedbysupplying adjoining track sections with alternating currents of oppositerelative polarity and interposing phase sensitive apparatus between thetrack rails and the track relayassociated with the track section, asshown in the above mentioned patent. However, suc track circuits havebeen found to be undesirable since certain defective components withinthe phase sensitive apparatus along with a defective insulated railjoint may also result in the improper operation of the track signals.

It is, therefore, an object of the present invention to overcome theabove mentioned difficulty.

A further object is to provide the track circuits associated with arailway signaling system with phase sensitive apparatus wherein thetrack signals are irresponsive to the flow of current from adjoiningtrack sections across a defective insulated rail joint even whencomponents within the phase sensitive apparatus are defective.

In accordance with my invention, I provide one end of each track sectionwith coded alternating current energy, and adjoining track sections areprovided with currents of opposite relative polarity. The opposite endof each track section is provided with a direct current relay which isconnected to the track rails through phase sensitive apparatus. Thephase sensitiveness is achieved through an unique arrangement wherebythe track relay is responsive only to currents applied to the trackrails having a predeterminedrelative polarity and is irrespons ive tocurrents of any polarity applied to the track rails when a componentwithin the phase sensitive apparatus is defective. Other objects of myinvention will appear hereinafter as the characteristic features ofconstruction and mode of operation of the apparatus embodying myinvention are considered in detail.

2,884,516 Patented Apr. 28, 1959 I shall first describe severalembodiments of my in; vention and shall then point out the novelfeatures thereof in claims.

In the accompanying drawings,

Fig. 1 is a diagrammatic view showing one form of phase sensitive trackcircuit embodying my invention employed in connection with a railwaysignaling system.

Fig. 2 is a diagrammatic representation of the operation of the phasesensitive track circuit shown in Fig. 1 whereby improper operation ofthe track signals is prevented.

Fig. 3 is a diagrammatic view showing a track circuit embodying myinvention provided with a filter circuit for reducing the effect offoreign currents flowing in the track rails.

Fig. 4 is a diagrammatic view of a track circuit embodying my inventionprovided with a second form of phase sensitive apparatus.

Fig. 5 is a diagrammatic representation of the operation of the phasesensitive apparatus employed in the track circuit of Fig. 4.

Fig. 6 is a diagrammatic view of a track circuit embodying my inventionillustrating the manner in which a single winding track relay may beemployed in connection with my invention.

In each of the difierent views similar reference characters are used todesignate similar parts.

Referring now to Fig. 1, there is shown a stretch of railway trackcomprising track rails 1a and 1b. The stretch of track is divided intotrack sections, two of which are designated by the reference charactersA and B. The track rails of adjoining track sections are separated byinsulated rail joints 2 and adjoining sections are electricallyconnected by means of impedance bonds. The impedance bonds comprisecenter tapped inductances 3 which are connected across the track railsat the ends of each section. The center taps of the inductances ofadjoining track sections are conductively connected by means or aconductor 4 to provide a return path for traction current.

Tratllc normally moves through the stretch of track in the directionindicated by the arrow, that is from left to right, and the movement oftraffic into each track section is controlled by a suitable signal,designated by the reference character S with a prefix corresponding tothe track section with which it is associated, located adjacent theentrance end of the track section. As shown, the signals are of thecolor light type, and each is provided with a red or stop lamp R and agreen or proceed lamp G.

Each track section is provided with a track relay located adjacent theentrance end of the track section and designated by the referencecharacter TR with a prefix corresponding to the reference character forthe track section with which it is associated.

The track relays are code following relays of the magnetic stick typeand may be equipped with a single winding having a center tap or as hereshown with two separate windings comprising coils a and b. The relaysare further provided with a movable member 4 which cooperates with fixedcontacts 5 and 6 in a manner so that, when the relay is energized in amanner soon to be explained, a circuit is alternately completed to eachof these contacts. The track relay controls slow releasing codedetecting relays designated by the reference characters FSA and BSA witha prefix corresponding to the track section with which they areassociated in such manner that the relay BSA is energized when, and onlywhen, the associated track relay is responding to coded energy. Therelay BSA controls the track signals so that the red or stop lamp islighted when the relay BSA is released and a green or proceed lamp islighted when the relay BSA is energized. Each track relay is connectedto the track rails through a phase sensitive apparatus, the operation ofwhich will soon be explained.

.A source of alternating current energy coded. at a suitable code ratefor operating the. track relay is connected to the opposite end of eachtrack section through a transformer designated by the referencecharacter T with a prefix corresponding to the track section with whichit is associated. A current limiting device 7, here shown as aresistance, is connected in series with a secondary winding 8 of thetransformer and the track rails to limit the flow of current through thetransformer at times when the track rails are shunted by the wheels andaxles of a vehicle within the track section. A primary winding 9 of thetransformer is connected through contact a of a code transmitter,designated by the reference character CT- with a prefix corresponding tothe track section with which it is associated, to a source ofalternating current energy 58. The circuit connections between thesource of current and the transformers of adjoining track sections arearranged so that the currents supplied to adjoining track sections areof opposite relative polarity. The code transmitters cause the tracksections to be supplied with alternating current energy which isperiodically interrupted at a suitable code rate for operating the trackrelay.

To prevent the track relay and associated track signals from beingoperated improperly due to current flowing across a defective insulatedrail joint separating two adjacent tracksections, phase sensitiveapparatus is interposed between the track relay and the track rails.This arrangement provides means for comparing the relative polarity ofthe current received at the relay end of the tracksection with currenthaving a predetermined relative polarity. If the currents received atthe relay end of the track section have the predetermined relativepolarity, the track relay is responsive, but if the received current isof opposite relative polarity the track relay is irresponsive. -Thismakes it possible to assure that the track relay is not responding tocurrent from an adjoining track section due to a defective insulatedjoint which would cause improper operation of the track signals;

'The phase sensitive apparatus comprises a track transformer 10, anauxiliary transformer 11, and a first and second rectifier designated bythe reference characters K1 and K2 respectively. Each track transformeris provided with a pair of secondary windings 13 and 14 and with aprimary winding 12 which is connected to the track rails. The auxiliarytransformer is provided with a primary winding 15 which is, preferably,connected through a phase shifting device 16 to the source whichsupplies alternating current to the track rails or to a source having afixed phase relationship with that source. The phase shifting deviceprovides means for adjusting the phase of the current flowing in theprimary winding and is here shown as variable resistance 16. Theauxiliary transformer is provided with a secondary Winding 17 which isconnected, in a series opposing relationship with the secondary winding13 of the track transformer 10, to the rectifier K1. The phase shiftingdevice 16 provides means for adjusting the relative phase of thevoltages induced in the secondary winding 17 of transformer 11 so thatthis voltage and the voltage induced in winding 13 of transformer aresubstantially 180 out of phase. This phase shift compensates for thephase shift of the track current due to the impedance of the trackcircuit. Winding 14 of transformer 19 is connected to rectifie'nKZ. Thedirect current terminals of rectifiers K1 and K2 are connected towindings a and b, respectively, of the track relay. Although therectifiers are here shown connected in a bridge arrangement, it is to beunderstood that other forms of rectifying circuits such, for example, asa single half wave rectifier may be employed.

j To provide an understanding of the mode of operation of the phasesensitive apparatus, reference is made to Fig. 2. There shown is a setof mutually perpendicular axes, hereinafter referred to as the abscissaand ordinate axes intersecting at a point to provide a four quadrantrepresentation of the operation and which quadrants intersect at acommon point referred to as an origin and represented by the referencecharacter 18. The abscissa axis represents the track voltage applied towinding 12 of the track transformer 10. Voltages to the right of theorigin represent track voltages having a definite phase relationshipwith the voltage induced in the secondary winding 17 of transformer 11,hereinafter referred to as the normal phase, and voltages to the left ofthe origin represent track voltages of the opposite relative phaserelationship and, hereinafter referred to as the reverse phase.Similarly, the ordinate axis represents the magnetomotive force producedby the windings of the track relay as a result of the track voltage.Magnetomotive forces above the origin represent magneto motive forcesproduced by the relay windings in one direction, hereinafter referred toas the normal or positive magnetomotive force, and magnetomotive forcesbelow the origin represent magnetomotive forces produced by the relaywindings in the opposite direction, hereinafter referred to as thereverse or negative magnetomotive force.

The voltages induced in winding 13 of transformer 10 and winding 17 oftransformer 11 cause a magnetizing force to be developed in winding a ofthe track relay ATR. This magnetizing force is represented" in Fig. 2 bya discontinuous line designated by 19-2G-21-22 which lies withinquadrants III and IV. Similarly, the voltages induced in winding 14 oftransformertlfl provides a magnetizing force for winding b of the trackrelay which is represented by the discontinuous line 23--182425 whichlies within quadrants I and II. These magnetizing forces combine in avectorial relationship to provide a resultant flux; that is, themagnetizing forces produce fluxes in opposite directions within therelay core which oppose each other. The resulting flux within the coreis represented on the diagram by a discontinuous line 2620-2427 whichlies within quadrants I, III and IV.

The armature of the track relay is moved to the normal position when,and only when, the resulting mag netomotive force produced by the relaywindings exceeds, in a positive direction, a magnetomotive forcerepresented by a broken line labeled normal pick-up. Similarly, thearmature is moved to the reverse position when, and only when, themagnetizing force exceeds, in a negative direction, that represented bya dotted line labeled reverse pick-up. Accordingly, if the relay is tofollow code, it is necessary that the relay be alternately energizedwith positive and negative magnetizing forces which are equal to orexceed the normal pick-up and reverse pick-up values respectively. It isthis feature which is responsible for the apparatus of my inventionbeing immune to currents feeding across defective insulated rail jointsto operate the track signals improperly, as discussed below, even whenparts are defective within the phase sensitive apparatus.

I shall presently describe the normal operation of the apparatusassociated with track section A in Fig. 1 and shall, thereafter,describe the behavior of the circuit in response to a defectiveinsulated rail joint.

At times when contact a of the code transmitter ACT is open, there is noenergy applied to the track rails and, likewise, no voltage induced inwindings 13 and 14 of the track transformer 10. Accordingly, there is nomagnetomotive force produced by winding b of the track relay ATR. Thiscondition would be represented in Fig. 2 by a point at origin 18. Thereis, however, a voltage induced in winding 17 of the auxiliarytransformer 11, which voltage energizes winding a of the track relay toproduce a magnetomotive force as indicated by the reference character20.in 1Fig. 2. Accordingly, theresultant or net magnetomotive force isindicated by the reference character 20. It, is seen that thismagnetomotive force, is sufiicient to'energize the track relay to itsreverse position.

{The track relay remains energized in the reverse position until contacta of the code transmitter closes, at which time alternating currentenergy is supplied to the track rails. This energy fiows alongthetrackrails to the track transformer 10, assuming the track section to beunoccupied. This energy causes a voltage to appear across the primarywinding 12 ofthe track transformer.

as illustrated by (+.E), locatedalong the positive abscissa axisin Fig.2. This voltage causes voltages to be induced in the secondary windings1 3 and 14. The voltage induced in winding 14 is' rectified by rectifierK2 and the rectified; current flows in winding 12 of the track relay.This current, in turn, produces a magnetornotive force asiindicated. bythe reference character ,29 in Fig. 2. Simultaneously, the voltageinduced in the secondary winding 13 of track transformer 10 and thevoltage induced in the secondary winding 17 of the auxiliary transformer11 combine to produce a resultant voltage and the resultant voltage isrectified by rectifier. K1. The rectified current energizes Winding a ofthe track relay to produce a magnetornotive forceas indicated by thereference character 30. The resultant magnetomotive force produced bythe windings is represented by the reference character 31. It is seenthat the resultant magnetomotive force is greater than the normalpickupvalue and, accordingly, thefrelay is energized to the normal position.Thus, as the track rails are supplied with coded currerit the trackrelay is alternately energized to the reverse positioniduring the offperiod of the code and to the normal position during the on period ofthe code. The code following action of the track relay causes themovable member 4 to periodically make contact with fixed contacts 5 and6 which, in turn, control the track signals to display, asdiscussedabove, a green or proceed indication for trafiic arriving atthe entrance of the track section. When the track section is occupied bya vehicle, the track rails are shunted which prevents the fiow' ofenergy from the supply end of the track sectionto the track transformer10. Insofar as the track relay isconcerned, this corresponds to thecondition, discussed above, inwhich contact a of the code transmitter isopen and, accordingly, the track relay is energized to the reverse pickup position as indicated by the reference character 20. Therelay remainsenergized in this manner'as long as the track section is occupied. Sincethe track relay is not responding to code during this time, the relaysAFSA and ABSA are deenergizedand a red or stop signal is displayed totraffic approaching the track section.

Having thus described the normal operation of the track circuitembodying my invention, I shall now consider the casein which a currentof the opposite relative polarity to that normally applied to the trackrails flows across a defective insulated rail joint from an adjoiningtrack section for the purpose of illustrating the inoperativeness of thetrack relay in response to currents of such polarity.

'Let it be assumed that an insulated rail joint separating tracksectionAfrom an adjoining track section'such, for example, as the track sectionto the left of track section A is defective and simultaneously tracksection A is shunted by a vehicle. This causes the track'section to besupplied with a current of opposite relative polarity to that normallysupplied to the section. In this case, the voltage impressed lupon theprimary winding 12 of the track transformer 10 is of the reversedrelative polarity to that considered above. in connection. with thenormal operation of the track circuit. This is shown in Fig. 2 by thereference character E) located along thenegative abscissa axis. Thenegative value merely indicates that this voltage is opposite inrelative polarity to the voltage normally applied tothis winding.Accordingl ,the voltages induced in the secondary windings are reversedin phase'to those normally induced in the windings. Since rectifier K2is not phase sensitive, the reverse polarity has no' effect upon themagnetomotive force produced by winding b of the track relay ATR,asshown by the reference character 32 of Fig. 2.. .However, the reversedphase causes the voltage induced in winding 13 of the track transformer10 to be in phase with that induced in the secondary winding 17 oftransformer 11. Thus, the magnitude of the voltage applied to rectifierK1 and winding a of the track relay increases, rather than decreases asdiscussed above in' connectionwith the normal polarity. J This causes amuch larger magnetomotive force to be produced by winding a of the trackrelay as shown by the reference character 33. The magnetomotive forceproducedby winding b is rep resented by the reference character 32andfthe'resultant magnetomotive force produced by thewindings is shownby the reference character 38. Thus, it is seen that, the net resultmagnetomotiveforce is suchto maintain the track relay in the reverseposition. Therefore, it is in this manner that the relay, and thus thetrack signals, do not respond to coded current supplied from anadjoining track section across a defective insulated rail joint.

At this point it should be noted that there is no fault which can occurwithin the track circuit apparatus which, in connection with a defectiveinsulated rail joint, can cause improper operation of the track relayand,'in turn, the track signals. This fail safe feature isextremelyimportant in connections with the use of track circuits in connectionwith signalingsystems of thetYPe in which my invention is intended to beused.

Often there are currents, other than signaling currents, which flowwithin the'track rails. These currents, referred to hereinafter asforeign currents are caused by a variety of sources such, for example,as traction current for vehicles in electrified territory orearthcurrents from commercial power stations and the like. .Insuch casesthese foreign currents may develop sufficient voltage across the trackrails at the relay end of the track section to cause improper operationof the track signals. It is, therefore, frequently necessary to providethe track circuit apparatus with means for preventing the foreigncurrents from affecting the tracksignals. My invention may be employedin connection with such means as shown in Fig. 3.

Referring now to Fig. 3, there is shown a track circuit embodying myinvention which is provided with filtering means for preventing suchforeign currents from affecting the track signals. Except for thefiltering means, the operation of the track circuit is similar to thatconsidered above in connection with Fig. l and, for that reason, theoperation will not be redescribed here except where necessary inpointing out the operation of the filtering apparatus. a

The filtering apparatus comprises a frequency selective network which isconnected between the track rails and the phase selective network. Thefiltering means, as here shown, comprises a transformer 34 provided witha primary winding 35 connected to the trackrails and a secondary Winding36. The secondary winding is connected in shunt with'a capacitor 37 andthe parallel combination is tuned to the signaling current frequency. Aportion of the secondary winding is connected through a second capacitor38 to a primary winding 39 of a second transformer 40. The secondcapacitor is tuned with the effective inductance of windings 36 and 39to the sig: naling current frequency. Inasmuch as these circuits aretuned to the signaling current frequency, currents of this frequency arepassed with little or no attenuation, but foreign currents havingfrequencies substantially different fron that of the signaling currentfrequency are attenuate The transformer 40 is provided with a secondarywinding 41 which is connected in a series opposing relationship withwinding 17 of the auxiliary transformer 11. The resulting voltageinduced in these windings energizes the rectifier K1 and winding a ofthe track relay ATR as described above in connection with Fig. 1.Rectifier K2 and winding b of the track relay are energized by thevoltage developed across a portion of the primary windingwhich isconnected to the relay in an autotransformer relationship, rather thanfrom a separate winding located on a track transformer as shown in Fig.1.

It is to be noted that alternating current energy is supplied to thetrack rails from the transformer AT through an impedance 42 rather thanthrough a resistance as shown in connection with Fig. l. The impedanceis used here not only to limit the current flowing through the secondarywinding 8 of the transformer when the track rails are shunted by avehicle, but also to produce a phase shift inthe current applied to thetrack section to compensate for the phase shift produced by thefiltering network as used in connection with the relay end of the tracksection. It is seen that this phase shift is necessary so that thevoltages induced into the secondary winding of the track transformer andthe secondary winding of the auxiliary transformer are in an opposingphase relationship as described above.

Another form of track circuit embodying my invention which may be usedin connection with an alternating current track circuit is shown in Fig.4. Insofar as the track signals are concerned, the operation of'thetrack circuitis similar to thatv discussedvabove'in connection withFig. 1. The differences between the circuits lies entirely within thephase sensitive apparatus. In the circuits, here shown, both windings ofthe track relay are normally biased with a magnetomotive force, evenwhen no energy is applied to the track rails.

A track transformer 43 is provided with two secondary windings 45 and 46and with a primary winding 44 which is connected to the track rails. Thesecondary windings are, preferably, provided with the same number ofturns. An auxiliary transformer 47 is provided with a primary winding 48which is connected through resistance 16 to the source of energy 58. Theauxiliary transformer is further provided with two secondary windings 49and 50 of which one winding, here shown as winding 49, is provided withmore turns than the other. Winding 45 of transformer 43 and winding 49of transformer 47 are connected in a series opposing relationship,through the rectifier K1 to winding a of the track relay ATR whilewinding 46 of transformer 43 and winding 50 of transformer 47 areconnected, in a series aiding relationship, through the rectifier K2 towinding b of the track relay. Resistance 16 in series with the primarywinding 48 of transformer 47 merely provides means for adjusting therelative phase of the voltage induced in the secondary windings oftransformer 47 with respect to those induced in the secondary windingsof transformer 43. This phase shift compensates for the shift in phaseof the current along the track section due to the track impedance, asdiscussed above.

Reference is made to Fig. 5 for an understanding of the mode ofoperation of the phase sensitive apparatus shown in connection with Fig.4. It can be seen that this diagram is very much similar to that of Fig.2 except for the differences discussed below.

It is to be noted that there is a magnetomotive force produced by eachof the windings of the track relay when there is no voltage applied tothe rails of the section. The magnetomotive force produced by winding a,when there is no track voltage, is represented by the referencecharacter 52 whereas that produced by winding b is represented by thereference character 51. The resultant magnetomotive force of bothwindings as represented by the reference character 53 is such toenergize the track relay to the reverse position. Thus, the track relayis maintained in the reverse position at times when either contact a ofthe code transmitter is open or when the track rails are shunted by avehicle. 7

During periods when contact a of the code transmitter is closed, avoltage represented by (+E) appears at the relay end of the tracksection, assuming the track section to be unoccupied. This causes avoltage to be induced in the secondary windings of the track transformer43. This voltage, being of normal relative polarity, induces voltages ofsuch polarity that winding b of the relay is provided with an increasedmagnetomotive force as represented by the reference character 29 andwinding a is provided with a reduced magnetomotive force as representedby the reference character 30. Under these con ditions, it is seen thatthe resultant or net magnetomo tive force as represented by thereference character 31 is such to energize the track relay to the normalposition. Thus, as long as the track rails are supplied with codedcurrent, the track relay will alternately be energized to the reverseand normal positions. The slow releasing relays AFSA and ABSA areresponsive to this action, as described above, to cause a green orproceed signal to be displayed to traflic approaching the track section.

At times when the track rails are shunted by a vehicle, there is novoltage induced in the secondary winding of the track transformer 43.Insofar as the phase sensitive apparatus is concerned, this provides anidentical magnetization of the track relay as exists when the tracksection is unoccupied and contact a of-the code transmitter is open.That is, the relay is energized with a magnetomotive force as indicatedby the reference characcharacter ter 53 in Fig. 5 and is sustained inthat position as long as the track rails are shunted by a vehicle.Accordingly, the relays AFSA and ABSA are deenergized and a red or stopsignal is displayed to traflic approaching the track section.

Again, for the purpose of providing an understanding of the manner inwhich this track circuit functions in protecting the track relay andsignals against the effects of a defective insulated rail joint, let itbe assumed that one of the insulated rail joints to the left of thetrack section A is defective and that, simultaneously, a vehicle isoccupying track section A. Energy from the track section to the left oftrack section A may flow across the defective insulated joint, asdiscussed above, to energize the track transformer 43. Since theadjoining track section is supplied with current of the reverse relativepolarity, that is opposite to that normally applied to the transformer,this may be represented in Fig. 5 by the reference character (-E)located along the negative abscissa axis. In this case the voltageinduced in Winding 46 of transformer 43 and winding 50 of transformer 47are substantially out of phase and the magnetomotive force produced bywinding b of the track relay is reduced as represented by the reference32 in Fig. 5. Similarly, the voltages induced in winding 45 oftransformer 43 and winding 49 of transformer 47 are substantially inphase to increase the magnetomotive force produced by winding a of thetrack relay to that represented by the reference character 33. Thereby,the resultant magnetomotive force, as repre sented by the referencecharacter 38, remains in the reverse pick-up region. Accordingly, ascoded current is supplied over a defective rail joint, the resultantmagnetomotive force merely alternates between the values indicated bythe reference characters 38 and 53 which are both in the reverse pick-upregion. Thus, the relay will not follow coded current of this relativepolarity and the track signals display a stop or red signal to trafficarriving at the entrance end of the track section.

It should be understood that the track circuit shown in Fig. 4 may beprovided with a filter network connected between the phase sensitiveapparatus and the track rails to prevent foreign currents which may beflowing within the track'rails from effecting the track signals. .Incases where a filter network is employed it maybe desirable to use animpedance at the feed-"end of the track circuit to limit the fiow ofcurrent rather than the resistance as discussed previously.

It may, at times,-be desirable to employ a single winding relay inconnection with track circuits of this type. My invention may beemployed with such relays as illustrated in Fig. 6. Referring now toFig. 6 it is seen that the circuit arrangement is similar to that shownand discussed in connection with Fig. 4, except for the connectionsbetween the track relay 54, which is a single winding relay, and therectifiers K1 and K2. For the purpose of illustration, assume that thetop terminal of each of the rectifiers is positive with respect to thebottom terminal as indicated by the polarity markings on the drawings.The positive terminal of rectifier K1 is connected to the negativeterminal of rectifier K2 through two resistances 55 and 56, connected ina series arrangement. The common junction of the two resistances isconnected to one end of the relay winding. The negative terminal ofrectifier K1 and the positive terminal of rectifier K2 are connectedtogether and, in turn, connected to the other end of the relay winding.Thus, the relay is energized with a polarity depending upon whichrectifier is supplying the greater rectified voltage. At times whencontact a of the code transmitter is open, rectifier K1 supplies thegreater rectified voltage to energize the relay with one polarity sincewinding 49 of transformer 47 is provided with more turns than winding 50and, accordingly, produces a larger induced voltage. ion/ever, whencontact a of the code transmitter is closed, voltages are induced in thesecondary windings of transformer 43, assuming the track section to beunoccupied, such that the voltage induced in winding 45 opposes thevoltage induced in winding 49 and the voltage induced in winding 46 aidsthe voltage induced in winding 50. This causes rectifier K2 to supplythe greater rectified voltage to the relay so that the track relay willbe energized with the current of the opposite polarity. Thus a singlewinding relay may be employed in connection with my invention.

While I have described my invention as used in connection with codedtrack circuits, it should be understood that the same track circuitarrangement may be employed in connection with non-coded signalingsystems. Moreover, while the drawings have shown the track section to beequipped with impedance bonds for electrified territory it should beunderstood that the apparatus may be used, equally as well, innon-electrified territory where impedance bonds are not employed.

While I have shown and described several forms of track circuits for arailway signaling system which embody my invention, it should beunderstood that various changes and modifications may be made thereinwithin the scope of the appended claims without departing from thespirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In a railway signaling system for a stretch of railway track in whichthe track rails are divided into sections by insulated rail joints, acoded track circuit for each track section comprising, in combination, asource of alternating current energy, coding means connecting saidsource and said rails at one end of each track section for supplyingcoded current thereto, a relay, a first transformer provided with firstand second secondary circuit means and with a primary circuit meansconnected to said rails at the opposite end of said track section, asecond transformer provided with a secondary circuit means and with aprimary circuit means connected to said energy source, said firstsecondary circuit means of said first transformer being connected inseries opposition with said secondary circuit means of said secondtransformer, a first rectifying means connecting said series connectedsecondary circuit means to said relay, a second rectifying meansconnecting said second secondary circuit means of said first transformerto s'aidrelay, and means controlled by said relay for indicating theoccupancy condition of said track section.

' 2. In a railway signaling system for a stretch'of railway track inwhich the track rails are divided into track sections by insulated railjoints, a coded track circuit for each track section comprising, incombination, a source of alternating current energy, coding meansconnecting said source and said track rails at one end of each tracksection for applying coded current thereto, a first transformer providedwith first and second secondary windings and with a primary windingconnected to the track rails at the opposite end of said track section,a second transformer provided with first and second secondary windingsand with a primary winding connected to said energy source, said firstsecondary windings being connected in a series aiding relationship andsaid second secondary windings being connected in a series opposingrelationship, a relay, rectifying means connecting said second secondarywindings to said relay, and means controlled by said relay forindicating the occupancy condition of said track section.

3. In a railway si naling system for a stretch of railway track in whichthe track rails are divided into track sections by insulated railjoints, a coded track circuit for each track section comprising, incombination, a source of alternating current energy, Coding meansconnecting said source and said track rails at one end of each sectionfor applying coded current thereto and with adjoining sections suppliedwith currents of opposite relative polarity, a first transformerprovided with a primary circuit means connected to the opposite end ofsaid track section and with first and second secondary circuit means, asecond transformer provided with a primary circuit means connected tosaid energy source and with a secondary circuit means, said firstsecondary circuit means of said first transformer being connected in aseries opposing relationship with said secondary circuit means of saidsecond transformer, a relay, a first rectifying means connecting saidseries connected secondary circuit means to said relay, a secondrectifying means connecting said secondary circuit means of said firsttransformer to said relay, and signaling means controlled by said relayfor indicating the occupancy condition of said track section.

4. In a railway signaling system for a stretch of railway track in whichthe track rails are divided into sections by insulated rail joints, acoded track circuit for each track section comprising, in combination, asource of alternating current energy, coding means connecting saidsource and said rails at one end of each track section for supplyingcoded current thereto, a relay, filtering means connected to the trackrails at the opposite end of said track section, a first transformerprovided with a primary winding connected to said filtering means andwith first and second secondary windings, a second transformer providedwith a primary winding connected to said energy source and with asecondary winding, said first secondary winding of said firsttransformer being connected in series opposition with said secondarywinding of said second transformer, a first rectifying means connectingsaid series connected secondary windings to said relay, a secondrectifying means connecting said second secondary winding of said firsttransformer to said relay, and means controlled by said relay forindicating the occupancy condition of said track section.

5. In a railway signaling system for a stretch of railway track in whichthe track rails are divided into sections by insulated rail joints, acoded track circuit for each track section comprising, in combination, asource of alternating current energy connected to one end of each tracksection, a relay, a first transformer provided with first and secondsecondary circuit means and with a primary circuit means connected tosaid rails at the opposite end of said track section, a secondtransformer provided with a primary circuit means connected to saidenergy source and assure with a secondary circuit means, said firstsecondary circuit means of said first transformer being connected inseries opposition with said secondary circuit means of said secondtransformer, a first rectifying means connecting said series connectedsecondary circuit means to said relay, :1 second rectifying meansconnecting said secondary circuit means of said first transformer tosaid relay, and means controlled by said relay for indicating theoccupancy condition of said track section.

UNITED STATES PATENTS Goff Oct. 27, 1936 Friedlander Nov. 28, 1939Talbert et al Nov. 22, 1945 Shipp Feb. 12, 1952 Mishelevich Jan. 12,1954

